Fiber transmission is very mature on both a technical level and a network application level; however, because of limitations such as landforms and topography, a wireless manner needs to be used for transmission in many places, and a microwave transmission manner is generally used in a case in which a large bandwidth is required. Currently, in applications in markets such as base station backhaul transmission of a mobile cellular system, networking between a transmission network and a metropolitan area network, a digital relay transmission network of a broadcast and television network, a dedicated network (such as a power network, or a military network) and large enterprise access, microwave transmission is widely applied.
In a microwave transmission communications system, frequently-used frequency bands are 1.4 GHz to 2.7 GHz, 3 GHz to 11 GHz, 23 GHz to 55 GHz and the like, a channel bandwidth is 0.025 MHz to 56 MHz, and a transmission rate may reach hundreds of Mbps.
With increases in service requirements, a microwave transmission system needs to develop towards higher-speed transmission communication. Spectrum resources of frequently-used frequency bands are limited, and therefore, if data needs to be transmitted at Gbps, multichannel communication, for example, a technology such as polarization multiplexing or multiple-input multiple-output (Multiple-input Multiple-output, MIMO), is a main development direction of microwave in the future.
In a microwave communications system, the impact of fading variation on system performance is usually reduced by controlling a transmit power. In an emerging multichannel communications system in the field of microwave communication, the foregoing problem also needs to be considered to reduce the impact of fading variation.
An Automatic Transmit Power Control (Automatic Transmit Power Control, ATPC) technology is widely applied in digital microwave communication. A key point of the technology is that an output power of a microwave transmitter varies automatically within a control range of the ATPC by tracing a variation of a receive level at a receive end. In a normal propagation condition, the output power of the transmitter is fixed at a relatively low level, for example, a level lower than a normal level by 10 dB to 15 dB. When propagation fading occurs and a receiver detects the propagation fading, a peer transmitter is immediately controlled by using a microwave band overhead byte, to increase a transmit power. The technology may desirably solve a problem such as fading variation in single-channel communication.
For a microwave multichannel system, a receive signal is usually susceptible to in-band interference from another transmit antenna, and an actually useful receive power cannot be accurately acquired. Therefore, the problem such as the impact of fading variation in the multichannel system cannot be solved by using the existing ATPC technology.